Privacy system



Nov. 20, 1934. D, MITCHELL PRIVACY SYSTEM Filed Marchl 3. 1933 2 Sheets-Sheet l 'H- fd 5-2\ B xNvENToR '11, Mac/ LL BY /SZ l ZTORNEY D. MITCHELL PRIVACY `SYSTEM Nov. 2o, y1934.

Filed March 3, 19:55

2 Sheets-Sheet 2 Relay 0,0 era ted liess t/zro tulo L Commutator .se

operatw//b une 5-57001 ape/ate e quick release relay ,agtnzen .Relay o/aerated W .mw 5t w z low Commutator se o/aerate -sZow release relay- ,qjast/melzt,

1Nv1-:NT 0R Mtchel BY ATTORNEY Patented ov. 20," 1934 PATENT OFFICE 1.981.113 -PRrvAcY srs-TEM Doren Mitchell, Martinsville, N. J., assignor to AmericanTelephone and Telegraph a corporation of New cYork Company,

Application March 3, 1933, Serial No. 659,559

8 Claims.

This inventionV 'relates to switching arrangements, and more particularly to switchingv arrangements for opening and closingv a number'of circuits, l

One of the objects of the switching arrangements of the invention is to provide means for connecting a device,1 such, for example, as al transmitter, to a transmission line over a number. ofv different circuits at' different times. A 10 further object of the switching arrangements of the invention, when used in connecting a transmitter to a line over different circuits, would be possible to have portions of the message overlap each other on the line. Adjustments in between these two are provided for with the switchingarrangements of the invention. In

general, the switching arrangements of the vin- 2.5 vention are applicable for al1 purposes wherein itis desired to open one circuit and to close another circuit in timed relationship with respect to each other. Other objects and features of the invention will appear more fully from the detailed description thereof hereinafter given.

An illustration of a specific system with which the switching arrangements of this invention might be used, would be a particular type of system for transmitting messages with secrecyl or privacy'.v Such a system is the subject matter of a copending application flled in the names of S. B. Wright and D. Mitchell on March 3,

1933, Serial No. 659,560. In'such a system pri- 40 vacy in the transmission of the message is secured by changing the order or position of the unitsof the'message from their original order or position at the transmitting end of the system. This accomplished by introducing va- 5 rious values of delay at the transmitting 'station by the switching mechanism of this invention. The units of. the message are then transmitted to a receiving station in the rearranged or scrambled order, and are not intelligible. At

the receiving end of the system complementary values of delay are introducedin a synchronous manner by the switchingmechanism of this invention, and the scrambled unitsl ofthe message .are rearranged in their original order or posi- 53 tion. A more detailed reference to this privacy lbranched paths 2 and 3.

(Cl. 179-15) v system will be given hereafter solely for the purpose of illustrating one of the uses to which the switching arrangements ofthe invention may' be put. However, it is to be understood that the switching arrangements of the invention are not limited to, use in this 'specic circuit but may be utilized ingeneral for all purposes where it isv desired to open and close a plurality of circuits in timed relationship with eachother.

The invention may be more fully understood from the following description'thereof, together with the accompanying drawings, in the Figures 1, 2, 3, 4, 5 and'6 of which the invention is illustrated. In Figure4 1 is a circuit diagram showing schematically a privacy 'systemutiliz- 70 ing 4the switching arrangements of the inven- `tion. Figs. 2 and-3 arediagrams-indicating the manner of scrambling and unscrambling 'the units of the message transmitted over a system such as shown in Fig. 1. Fig. 4 is a more 75 detailed circuit diagram showing the switching arrangements of the invention as applied to a portion of the system shown schematically in Fig. 1. Figs. 5 and 6 are diagrams illustrating dilerent methods of adjustment of the switohing device of the invention as sho-wn in Fig. 4. Similar reference characters have been utilized to denote like parts in certain of the figures.-

In Fig. 1 is shown a one-way telephone L interconnecting a sending station A and a receiving station B, and` utilizing switching arrangements for privacy purposes. At station A is shown \a transmitter 1 connected to' two In these branched paths would be included the switches S1 and S2 90 for opening and closing these paths. These switchesy are shown controlled by the relays 6 and '7 and by the commutator 8. The two branched paths are lthen connected to the line L.A Other means vfor opening and closing the two l branched paths such as the switching arrangements of the invention shown in Fig. 4, could be utilized in placeof the relays and switches, if desired. In the path 3 would be provided a delayv circuitv` D. At the receiving station B the line L would be connected to the two branched paths 10 and 1'1. To open and close these paths there would be provided the switches S'z and S1 controlled by the relays 14 and 15 and the commutator 161 'The two paths would be con- 105 nected to a telephone' set 9. In the path 10 vwould be provided a delay circuit D' equal to amount T. The commutators'S and 16 will re 1.10

volve at a speedof one revolution per T. The

two'commutators willbe operated in synchronisin by any well known means. It may be desired to have commutator 16 lag slightly Ibehind 8 to compensate for the delay d introduced by transmitting the message over line L.

The diagrams of Figs. 2 and 3 indicate how the arrangements of Fig. 1 operate to scramble the order of transmitted message sounds and restore them at the receiving end. For simplicity, it has been assumed that the originalmessage lasts for a time 2T. It is then divided into four units of equal duration equal to T/2. These are indicated in the top line of the time diagram of Fig. 2. The units are in their original order and are shown in the timed relationship in which they arrive at switch S2. The time of each individual unit is as pointed out heretofore one-half the length of time T introduced by the delay circuit D; vThe original units arriving at switch S1 will be delayed by Tand the time relationship in which they arrive thereat is shown in the second line of the diagram. For transmission onto the line there is then a choice between the undelayed or original message and the delayed message. The two segment commutator 8 is revolving once per time T. Thus at onehalf T the segment with battery connected thereto causes path 2 to be closed and causes path 3 to be opened. Since' path 3 was closed during the rst one-half T of time nothing has been transmitted onto the lineup to that instant due to the inclusion in path 3 of the delay circuit D. Thus it will be seen. 'hat when S2 closes, part or unit 2, of the message `will be the rst to be transmitted overline L. At time T, however, the commutator has made' a complete turn and path 3 with the delay therein is again closed and path 2 is opened. This causes the rst part of the message, or unit 1, to be next transmitted on the line L since it has been delayed by time T. This process is carried on indenitely although shown in the diagram for only four units. The result is that the message units are transmitted over the line in rearranged order, such as 2, 1, 4, 3,- etc., instead of 1, 2, 3, 4. This is shown in the lower line of the diagram.

As heretofore pointed out at the receiving station B, there will be provided a delay circuit D' similar to D and introducing Aa delay T. The commutator 16 will be' rotating at the same speed as 8 but retarded in angle by an amount to compensate for the delay d introduced by the line L. The diagram of Fig. 3 shows how the scrambled units of the message are restored to their original form. The rst unit of the scrambled message arrives at S1 at a time The time of arrival and order of these scrambled message units is shown in the-top line of the diagram as 2, 1, 4, 3. The time of. arrival at S'z of the scrambled units delayed T by D' is shown in the second line of .the diagram. At the time the scrambled units. start arriving, however, the' commutator will have `made one half turn and path 10 with delay D therein will be closed and path 11 opened. Attime rT-i-d, path 11 will again be closed and the path l0 with delay D opened. Accordingly', the rst message unit to reach the receiver will be unit .1. Next path 1 0 will be closed and unit 2 will be transmitted to the receiver. This process that the message units will be delivered to the receiver in their original order. This is shown. by the last line of. thel diagram.

In Fig. 4 the switching arrangements of the invention are shown as applied to the transmittingstation A of the system of Figfl.

In Fig.

4 is shown a telephone transmitter'l connected to two branched paths 2 and 3, and these paths are connected to line L through the switching-v arrangements comprising the push-pull ampli.

cuit over its contact from battery 21 through the low pass filter 22 'and through resistance R4 to ground. Due to the drop in R4 the negative bias applied to the push-pull amplifier S2 from battery 24 will be reduced when relay 19 is operated. This will allow transmission to pass through the push-pull amplifier circuit S2 and will effectively close line 2. In like manner, wh'en relay 20 is Aoperated a circuit will be closed from battery 21 through -the resistance R5. The drop in resistance ARe, will reduce the negative bias applied from battery 25 to the push-pull amplifier. S1 and allow it to become operated. Thus, it will be seen that the operation of relay 20 will effectively close the'circuit 3. the release of relay 19 willrestore the negative bias of battery 24 to thevpush-pull amplifier S2 and disable it. -This will effectively open the circuit 2. In like manner, the release of relay 20 will disable the push-pull amplier S1 and effectively open the circuit 3.

With the switching arrangements of the invention as shown in Fig. 4, it is apparent that circuit 2 may be closed and circuit 3 opened, and vice versa, as desired. Furthermore, the arrangements of the invention'provide great flexibility in controlling the quality or characteristics of the message transmitted over the lines 2 and 3. For example, gaps may be caused between portionsof the message which are sent (out from the transmitter 1. This may be accomplished by increasing resistances R and R1 (R2 and R3 are assumed to be very small in this case). Increasing resistances R and R1 will cause the relays 19 and 20 to become eectively slow operate, quick release relays. This is because condenser C and C1 will have to be discharged through resistances R and R1 before relays 19 and 2,0 can operate respectively. Relays 19 and 20 will release comparatively quickly however since condensers Cn and C2 will charge up comparatively quickly through resistances Rz and R3 and the relay windings since R2 and R3 and the resistances of vthe relaywindings are low compared to resistances R and R1. This means that at the beginning of each ground impulse from the commutator 18 relay 19 or relay 20 does not operate for a short interval. Thus, transmission through the vacuum tube circuit under consideration does not take place immediately. Eventually, however, the relay operates and enables its vacuum tube circuit, thus allowing transmission to pass therethrough. At the end of the impulse yfrom the commutator 18 the relay will release very quickly, thus quickly disabling the vacuum tube circuit under consideration. An impulse will be transmitted almost im Obviously,

the relays will not have time to operate during thel pulse sent from the commutator.

The manner in which the arrangementsof the invention introduce gaps between portions of `the message will be more clear from an' inspection of the diagram in Fig. 5. .The vertical dotted lines indicate the time when the ,commutator segment changes from one relay circuit to another. With theresistances R and R1 increased the relays 1'9 and20. will be slow operate, Vquick'release relays, and hence, will not foperate luntil a period after the commutator closes a.

circuit therefor. The operation'of the relays in this connection is indicated by the shaded portions in the upper part of the diagram. In the lower portion of the diagram are shown two curves S1 and S'z winch indicate the loss through the tube circuits S1 and S2. It will be seen that with the relays operating slowly and releasing quickly, that there will be certain peaks of high lossy such as betweenv the points ab, ab, etc. This will' cause the existence of gaps between portions of the message.

These gaps can be decreased and the portions `of the message can be caused to overlap by 'reducing R and R1 practically to zero and increasing the resistancesv R2 and Rs. This causes the relays 19 and 20 to operate immediately when their circuits are grounded by the commutator,

Ibut causes them to be slow in releasing after :the ground has been removed from their circuits. In this' case the condensers are discharged rapidly through resistances R or R1 but charge up gradually through resistances Ra and R3 and the relay windings since Rz and Ra are now large compared toV R and Ri.- This means that the vacuumtube circuit controlled by. a relay is enabled very shortly after the relay circuit is grounded and remains enabled after the ground is removed, for a short time, depending on the size of R2 or Ra. Thus, byincreasing R2 and R3 the point will first be reached where one vacuum tube circuit is enabled just up to the time when the other vacuum tube circuit be- `comes enabled. It will also be seen that by increasingresistances Rz andRa still further, various increasing amounts of overlap may be obtained up to thep'oint whereboth relay 19 and relay 2l? would beV operated continuously, since they would remain operated between the times that their circuits are grounded.

The method of causing Portions of the speech to overlap w appear more fully from an inspection o f the"diagram of Fig. 6. As pointed Iout, the adjustment of resistances R2 and Ra, has now made the relays quick operating. ,slow

release: relays. Their operation, with respect Ato the operation of the commutator segment, -is indicated by the shaded portions inthe upper part of the figure. The loss through the tubes is likewise indicated by the curves S'1 'and S'z. vIt will be seen that there exist no peaks f high loss with this arrangement.

The low pass lters 22` and' 23 have been prolvided in the circuit through ,which the current from. battery 21' 'must ow in order to lcause a current in resistances R4 and Rs', 4and thus cause a positive voltage to be' applied to the grids of the vacuum tubes. These lters smoothl oi lthe square impulse caused by the operation or release of relay 19 or relay 20. This means that the attenuation of vthe transmission circuits is changed gradually depending onthe number oi sections and the cu'tci of the low pass iilters. This may help to improve the quality of trans mission by preventing clicking or disturbing noises from being transmitted.` ln place of low pass iilters any desired shaping network could be used to change the square shape ci the impulse in any desired manner.

What is claimed is:

1. A switching system for effectively opening .and closing a plurality of circuits in timed rel lationship 'with respect to each other comprising a ilrst circuit, a vacuum tube device included therein, a second circuit, a vacuum tube device included therein, said tube devicesbeing normal- .ly disabled, relays individual to each of said tube devices for controlling 'the operativeness there of, means for regulating the speed or" operation and release of said relays, and switching means for closing operating circuits for relays.

2. A switching system for eiectively opening and closing a plurality of circuits in timed relationship with respect. to each other comprising g a rst circuit, a vacuum tube device included therein, a second circuit, a vacuum tube device included therein, means for applying a negative bias to the grids of each ci tube devices to cause them to be inoperative, relays individua?. to each of said tube devices, :means controlied by each of said relays when operated for reducing vtube amplifier included therein, and switching means comprising slow-operate quicio-release relays for gradually rendering one ci said amplifiers operative and rapidly rendering the other .of said ampliiiers inoperative. after the operation of lsaid switching means.

4i. A switching arrangement for effectively opening and closingA a plurality of circuits in ltimed relationshipv with respect to ,eachother comprising a iirst circuit, a vacuum tube amplifier included therein, a second circuit, a vacuum tube 'ampliiier included therein, and switching means comprising quick-operateA slow-release relays for rapidly rendering one of said ampliico ltd

mit..

ers operative and gradually rendering the other of said amplifiers inoperative after theoperation of saidl switchinguneans.

5. A transmission line, ltwo circuits connected thereto and in parallelfwith each other, means for simultaneously applying to said circuits units of a message similar to each other `in the frequency range, and quick-operate slowrelease relay means for causing the units applied from said circuits to said line to overlap each other by any desired amount.

6. A transmission line, two circuits connected thereto and in parallel with each other, means for simultaneously applying to said circuits units of a message similar to each. other in the frequency range, and slow-operate` quick-release relay means for causing gaps of any desired amount to exist between the units applied from said circuits to said line.

7. A switching system for. effectively opening and closing a plurality of circuits in timed relationship with respect to each other comprising a rst circuit, a vacuum tube device included therein, a second circuit, a vacuum tube device included therein, means for applying a negative bias to the grids of each of said tube devices .to cause .them to be inoperative, relays individual to each of said tube devices, means controlled by each of said relays when operated for reducing the negative bias applied to its associated tube device to cause it-to operata, operating oircuits for each of said relays, means for adjusting the constants of said operating circuits so that the speed of operation and release of said relays may be regulated, switching means for opening and closing said operating circuits, and networks included in each of said operating circuitsj said networks having characteristics whereby the gain of said tube devices will be changed gradually. A

8. A switching system for-effectively opening and closing a plurality of transmission circuits in timed relationship with respect to each other comprising a rst circuit, a vacuum tube device included therein, a second circuit, a vacuum tube for opening and closing said operating circuits,v

and ilters included in each of said operating circuits, said iilters having cut-off characteristics ,whereby the gain of said tube devices will bev changed gradually and transient noises reduced in said transmission circuits. v DCREN MITCHELL.

fir 

